Chocs Away!

Chocolate has long been a passion of mine. So much so that my GCSE English speaking presentation was on the subject. Sadly for me, but fortunately for you, dear reader, the content of said work has long been lost somewhere in the unsalvageable hard drive of an ancient computer, so cannot be easily regurgitated here. However, morsels still remain in my memory and my alleged development as a scientific researcher may help in producing something ever-so-slightly better than my 16 year-old self could manage. Although I gave out actual chocolate samples in my presentation, so I am not entirely sure about that…

I’ll start with a little bit of botany, with a twist of geography for good measure. Chocolate is made using the beans from the cocoa tree, Theobroma cacao. This is indigenous to the Central and Southern American tropics and is one of 22 species of Theobroma, whose name means “food of the Gods.” You will possibly have seen a specimen at the Botanical Gardens, or on your Gap Yah, if you did such a thing. Recently, scientists have been using genetics in order to track the spread of plant and its cultivation and domestication. They have found 10 distinct genetic clusters, separated largely by geography. Interestingly, the most genetic diversity is found in the Upper Amazon region, indicating that this is where the species originated. However, the question of when the tree was domesticated and cultivated for use is a contentious issue, but vessels which could have been used for an early version of the fermented cacao drink favoured by the Aztecs have been dated back to approximately 3500 years ago. However, this may not signify true domestication, rather semi-cultivation. Some rather excellent scientists who use analytical chemistry to analyse ancient pottery and have found that dry residue from Mokayan (Mesoamerican settled villagers) pottery vessels contained theobromine, which is a remarkable compound found in chocolate (see below) and a clear indicator of its presence. These vessels were dated from around 1900BC, so it’s clear that chocolate has been used in one form or another for a very long time.

The Spanish Conquest of South America resulted in the spread of chocolate to Europe and beyond. Upon their arrival, Cortez et al will have found a very different form of chocolate to that which we are used to today. The Aztecs tended to use their chocolate in drinks, in which the beans were ground, mixed with maize and peppers and fermented, which must have been a strain on the European palate. Having said that, many Europeans (Brits, I’m looking at us) are known for a taste for alcohol so it might not have gone down too badly! However, upon coming to Europe, chocolate was, although still used as a drink, more often mixed with vanilla and sugar to make it more palatable. The production of solid chocolate in Britain began in the 18^th Century, and involves more interesting science.

The production of chocolate requires extreme precision. There are a number of processes the cocoa beans must go through to be turned from brown, shrivelled, bitter droppings into velvety smooth richness, each of which has a specific purpose. After they have been harvested, the beans are fermented and dried, giving them their dark brown colour. They are then roasted to intensify their flavour, before winnowing to remove the edible nibs from their husk. These nibs are ground to form cocoa liquor, or cocoa mass, which is processed further to give two separate products: cocoa butter, used in chocolate, and cocoa presscake, which forms cocoa powder. The cocoa butter is mixed with additional cocoa liquor to form chocolate and has to undergo substantial processing to achieve the correct consistency and flavour, which is where the science comes in. The chocolate must first be conched, which is much like kneading and serves to effectively emulsify the fats within the chocolate, meaning that the cocoa butter is evenly distributed throughout. Furthermore, this process helps to develop flavour by eliminating some unwanted chemicals, such as acetic and butyric acids. The conching is done at a temperature specific to the chocolate being made (49-82⁰C), with higher temperatures reserved for darker chocolate. A higher temperature promotes the Maillard reaction, which results in a caramelised flavour in many foods. Amino acids and sugars react to form many different flavour compounds unique to the food undergoing the reaction.

After conching, the chocolate is tempered, which is another temperature controlled-process. This is of importance to the texture, rather than flavour, of the finished product. The melted chocolate must be cooled to 28⁰C, heated again to a temperature specific to the type of chocolate you are using (27-32⁰C). This is because chocolate crystallises in six different forms, and only one of these gives the right texture to give the smooth,  shiny, snappable product we (I) expect. This form is the beta form, or form V, and consists of small crystals. All of the other forms give a crumbly, rough, dull mess. Chocolate that isn’t “in temper”-as the pros call it- also suffers from the phenomenon known as fat bloom, where the fats rise to the surface and cause a streaky, mottled, dullness. A similar phenomenon occurs in my brain from time-to-time, I’m sure.

The production of chocolate clearly involves some fascinating scientific morsels, but there is also a lot of great science to be found within the reason for its sheer excellence: its exquisite taste. Chocolate is home to 600 volatile flavour compounds, which contribute to its unique flavour. 25 of these were found to be at a high enough concentration to be recognised by human olfactory receptors. These comprise of some very odd compounds which one would not necessarily associate with the flavour of chocolate, such as dimethyl trisulfide, which smells like cooked cabbage and 2- and 3-methylbutanoic acids which both smell rather sweaty. Dr Peter Schieberle, a researcher at Munich Technical University, found that combining these 25 compounds produced an aroma which was able to be identified by humans as chocolate! Fascinatingly, the interaction of just 4% of the flavour compounds found in chocolate with the olfactory neurons is sufficient to convince the human brain that it is smelling chocolate. Schieberle intends to use his work to tweak the chocolate making process in order to improve its flavour profile. I didn’t stumble across much about the other 575 flavour compounds in my (extensive and laborious-ish) research, but I am guessing that they all contribute to the unique tastes of different blends and brands. Something to look into on a rainy day, perhaps?

The flavour compounds in chocolate aren’t the only interesting ones it contains. I mentioned theobromine above, which is a signature compound of chocolate. This is a xanthine alkaloid, meaning that it belongs to the same chemical family as caffeine and is also a metabolite of caffeine, which is broken down by the liver into theophylline, theobromine and paraxanthine. Much like caffeine, it is a diuretic and a vasodilator (widens blood vessels). The compound was discovered in 1841 by Alexander Voskresensky and its vasodilatory properties mean that it has been used to treat high blood pressure, as well as arteriosclerosis (clogged arteries) and angina. So you read it here first- chocolate is good for you! It’s also an aphrodisiac- wink wink- and a reason why dogs and cats shouldn’t eat chocolate. They metabolise theobromine slowly, so the accumulation poisons them. Not so great.

Theobromine

There is so much more to explore regarding chocolate and health, as well as the science behind all aspects of this wonderful stuff, but I’ll let you have a break. I hope you have enjoyed my bounteous knowledge on the subject. To those of you who have reached the bitter end, I salute you. Hopefully now you will be chock full of fantastic facts with which to bore all of the people who leave a bitter taste in your mouth. Until next time… chocks away!

References:

Powis, T.G., et al, Antiquity, 2007, 81 (314) http://antiquity.ac.uk/projgall/powis/index.html, Clement, C.R. et al, Diversity, 2010 2, 72-106; doi:10.3390/d2010072

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0003311
http://www.sfu.ca/geog351fall03/groups-webpages/gp8/prod/prod.html
http://www.icco.org/about-cocoa/processing-cocoa.html
http://www.scientificamerican.com/article/sensomics-chocolate-smell/
Dr Peter Schieberle presented his work at a meeting of the American Chemical Society: http://www.acs.org/content/acs/en/pressroom/newsreleases/2011/august/whats-really-in-that-luscious-chocolate-aroma.html

Pongy Ponderings

This is a bit of a cheat, but here is an article I wrote for my college magazine (following "Going Bananas"). I thought it was about time I added to my oeuvre and posted it up here. Enjoy!

Commissioned once again by our illustrious editor to get my geek on and bring more pithy and zesty morsels (see what I did there?) of culinary science to the discerning readers of Linacre, I happily agreed, confident that my ability to bulls**t about things I really know nothing of had not deserted me or been used up on my extended essay. However, later contemplation served to instil a deep and very real fear, nay, panic. Writer’s block! How to top the giddy heights of last term’s column, for which I had received such compliments as “I like bananas,” and “I saw your name- I’ll read it later?” What subject could possibly provide as much entertainment and pure comedy as the banana, that funniest of foods; comic trope and device recognised internationally as truly hilarious? The answer, I realised, with a sinking feeling in my stomach, is nothing. So, like the inferior second season of a once- sparkling sitcom, clearly acknowledging that I have peaked but desperately clinging to one last shot in a ratings war which I will surely lose, I am opting for the easy way out: gross-out humour. The last resort of the desperate comedian. There is no dignity in this, but, as our aforementioned illustrious editor has pointed out, my sense of humour is akin to that found in a 12 year old boy, so I know that I am not above this task. Therefore, the subject of this lacklustre, trying-too-hard and probably not even remotely interesting (it’s page-filler, basically) article is the science of smelly food.

Improbable as it may seem, there are actually quite a number of scientists who trouble themselves professionally with this, delving into their compost bins and furking about in the bottom of the fridge (well, I imagine it’s actually a bit more sophisticated than that, but you get my drift) to find out what the molecular source of the pongs and whiffs therein actually is. Onions and garlic are extremely popular amongst sulfur chemists, although I imagine not with their significant others, as the cause of their odour is a family of sulfur-containing compounds which are modified during cooking to alter the smell from eye-wateringly offensive to mouth-wateringly appetising. In the 1980s, scientists found that the compound in raw onions with which this odorous journey begins is an amino acid derivative called propenyl cysteine sulfoxide. Slicing the onion exposes this unfortunate chemical to an enzyme called alliinase, which breaks it down into propenesulfenic acid and the mayhem begins. Two molecules of propenesulfenic acid can combine to produce thiosulfinate which is responsible for that pungent raw onion smell, whilst cooking produces the taste bud-tingling aroma of bispropenyl disulfide. (On a side note, it is very pleasing to meet a pleasant-smelling sulfur compound. I am currently working with carbon disulfide and as such am the least popular chemist in my lab. **Sob** I can only imagine what the guys who work on this onion and garlic business go through. They must be even less popular than the physicists.)

So, that’s the vegetables, but what about the smelly proteins? Meat, fish and eggs all suffer from their own personal hygiene issues, as it were. In the case of eggs, the culprit is once again sulfur, in the form of hydrogen sulfide (H₂S), and this is not only found in rotten eggs. According to eHow (yes, my research methods are once again exemplary), boiling eggs the wrong way can also cause a pongy problem. Overcooking produces excess hydrogen sulfide, which reacts with iron in the egg yolk. This is the cause of the smell and also of the greenish colour that rings the egg yolk of an imperfectly hard-boiled egg. Good to know. On another side note, typing “rotten egg smell” into Google turned up this rather wonderful gem from The Independent: “How the smell of rotten eggs makes men randy.”  That’s right. Apparently, tiny quantities of hydrogen sulfide are released in penile nerve cells and may stimulate an erection, which could present an alternative treatment route for people suffering from erectile dysfunction who don’t respond to Viagra. I’ll let you form your own opinions about this, but if you are, by any chance, interested a) don’t tell anyone- they may make certain assumptions and b) look the paper up- it’s been published in PNAS (that’s the Proceedings of the National Academy of Sciences).

Well, that was quite a detour, so back to the original point. At this juncture we wish sulfur farewell, as there are other molecular offenders who deserve a little mention in this missive. The chemicals responsible for the stomach-turning smell of rotten meat and fish and pungent cheese are, in fact, nitrogen-containing. Fish flesh contains a compound called trimethylamine oxide, which is broken down upon decomposition to give nasty smelling tri- and dimethylamine, making it very easy to tell whether the fishmonger was lying or not when he told you that the fish you bought was freshly caught 3 hours ago, but very difficult to make your fridge smell nice again. Likewise, the nitrogen-containing molecule present in rotting flesh of the meat variety is aptly (but disturbingly) named cadaverine and is a diamine produced upon the breakdown of the amino acid lysine. And we have all experienced the gag-inducing whiff of ammonia (NH₃) emanating from a somewhat over-ripe wheel of brie. I am not only beginning to feel very sorry for the sad reputation sulfur has despite nitrogen’s equal culpability in this field, but also praying to the chemistry gods (or my supervisor) that I don’t have to start working with amines any time soon.

So there we have it, dear reader. Apologies if you began reading this column over breakfast (particularly if that breakfast contained fish or eggs). I hope that, in such a case, you can forgive me for this woeful attempt at a follow-up on the glory days of Hilary term and take comfort in the fact that you will be beginning your day marginally better informed on a subject with no practical use whatsoever. That’s kind of how I feel about my PhD…